A common way for computers to communicate with each other over telephone lines is to employ modulator/demodulators ("modems"). For transmission, modems translate the computer's baseband digital signals to modulated-carrier signals that lend themselves to propagation over voice-grade telephone lines, and on reception they translate the carrier signals back again to the baseband signals that the computer recognizes.
Although analog circuitry has traditionally predominated in modems, attempts have been made more recently to take advantage of the superior reliability, repeatability, and flexibility that digital-signal-processing circuitry can provide. Advances in digital-signal-processor power have supported this trend, but the fact remains that performing modem functions digitally is decidedly computation intensive. As a consequence, modem designers have expended a great deal of effort to minimize the computational cost of digital modem operation. This effort has understandably tended to be concentrated on the modem's signal-processing aspects.